Apparatus and Methods for Movable Megasonic Wafer Probe

ABSTRACT

Methods and apparatus for a movable megasonic wafer probe. A method is disclosed including positioning a movable probe on a wafer surface, the movable probe having an open bottom portion that exposes a portion of the wafer surface; applying a liquid onto the wafer surface through a bottom portion of the movable probe; and moving the movable probe at a predetermined scan speed to traverse the wafer surface, applying the liquid to the wafer surface while moving over the wafer surface. In additional embodiments the method includes providing a transducer for applying megasonic energy to the wafer surface. Apparatus embodiments are disclosed including the movable megasonic wafer probe.

BACKGROUND

A common requirement in current advanced semiconductor processing is forwafer rinse and clean processes. Wafer rinse or clean is performed atvarious stages in the processing and may remove particles or residuesleft by a prior process. For example, patterned films such as dielectriclayers may be cleaned to remove particles. While in past generations ofsemiconductor tools, a batch rinse station might be used which appliedde-ionized water (“DIW”) or other cleaners to a number of wafersarranged in a boat or carrier by spray or immersion techniques, morerecently single wafer cleaning stations have been used. As wafer sizesincrease to the current 300 millimeter (“12 inch”) and the coming 450millimeter (“18 inch”) sizes, the use of single wafer tools is becomingeven more prevalent.

In the current single wafer cleaning tools, a wafer may be mounted on aplaten or chuck with its active face oriented upwards, for example, anda spray nozzle may apply deionized water (“DIW”) or other cleaningsolutions or solvents under pressure. The spray nozzle may travel acrossthe wafer. For example if the wafer is rotating about a central axis,the nozzle may travel rectilinearly across half or all of the wafer toenable the nozzle to spray the entire wafer surface. The speed thenozzle travels relative to the wafer surface is the nozzle “scan speed”.However, the use of pressure provided, for example, by aerosol and DIWsprayed on a wafer surface by a moving spray nozzle can damage wafers.In some systems, the nozzle pressure can be controlled and raised andlowered. However, even when low pressure is used, “outlier” dropletsfrom the spray nozzle can still impact the wafer surface at greatervelocity than desired, which may cause pattern damage. These fast movingoutlier droplets can transfer their kinetic energy to a loose particle,which as it travels away from the wafer surface, may collide with aportion of the pattern and damage the pattern. A lower nozzle spraypressure may be used to avoid the damage, but this lowered pressureresults in lowered particle removal efficiency. That is, a tradeoffexists in conventional wafer cleaning tools between the velocity ornozzle pressure of the spray DIW, and the particle removal efficiency(“PRE”) obtained.

A continuing need thus exists for methods and apparatus for cleaningwafers with high particle removal efficiency and without thedisadvantages currently experienced using known methods.

BRIEF DESCRIPTION OF THE FIGURES

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 depicts in a cross-sectional view an embodiment;

FIG. 2 depicts in a cross-sectional view the embodiment of FIG. 1 in usein an embodiment method;

FIG. 3 depicts in a cross-sectional view another embodiment;

FIG. 4 depicts in a cross-sectional view the operation of an embodimenton a wafer; and

FIG. 5 depicts in a flow diagram a method embodiment.

The drawings, schematics and diagrams are illustrative and not intendedto be limiting, but are examples of embodiments of the invention, aresimplified for explanatory purposes, and are not drawn to scale.

DETAILED DESCRIPTION

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

Embodiments of the present application which are now described in detailprovide novel methods and apparatus for providing a wafer cleaningsystem including providing a movable megasonic cleaning probe. Themovable megasonic cleaning probe is smaller in area than the wafer andmay travel around or across the wafer and thus “scan” the front side ofa wafer. The movable cleaning probe uses sonic energy such as megasonicenergy in addition to applying DIW or other cleaners or chemicals toremove particles. In some embodiments, the apparatus may also include abackside cleaning process that operates to clean the backside of thewafer simultaneously during the front side wafer processing. In someembodiments, the movable cleaning probe includes a port for applying thefluid, and further provides fluid circulation so that particles that aredislodged are immediately removed from the surface of the wafer; therebypreventing recontamination issues. By utilizing a movable immersion hoodapproach, the embodiment movable probe may apply process chemicals to awafer surface, replacing spray hoods and other known methods.

To achieve an efficient particle removal without damaging the delicatestructures formed on the wafer, the cleaning process needs to controlthe scan speed (and if used, wafer rotation speed) precisely. Furtherthe particles loosened, for example by megasonic energy, need to beefficiently removed to prevent these particles from re-depositing on thewafer. Accurate control of the scan speed and scan coverage pattern isimportant because the particle removal efficiency obtained needs to beas high as possible but without causing damage to the structures on thesurface of the wafer.

FIG. 1 depicts in a cross-sectional view an example embodiment of themovable megasonic probe 11. A transducer 13 is arranged in a centralportion of a body of immersion hood 15. Transducer 13 has an openingforming an input port 19 in a central portion and is spaced from theinner walls of the body of the immersion hood 15 by additional port orports 21. A bottom portion 17 of the immersion hood provides a foot orbuffer for contacting the wafer surface. The movable megasonic probe 11has a length “L”. The probe may be a couple of inches in length andwidth, or the length and/or width may be increased up to several inchesor more; typically, it is sized to cover a convenient portion of thesurface of a semiconductor wafer at the bottom opening 23. As wafersizes are now approaching 450 millimeters or 18 inches in diameter, themovable probe can be several inches long and still cover only a portionof the wafer at a time. The bottom opening 23 will be placed over thesemiconductor wafer and the wafer surface will form with the bottomportions 17, and the body of the immersion hood 15, and a fluidrecirculation path, as is described further below.

FIG. 1 is a cross-sectional view. The movable probe 11 may be, forexample, round or circular in shape; rectangular, octagonal, square, orother shape as desired. The materials should be durable materials suchas are used in tools for semiconductor processing. The transducer may bemade of a metal such as aluminum; a variety of alternative materials maybe used. Also these same materials may be used with immersion hood 15and bottom portion 17; in addition to aluminum, other durable metals andcompounds could be used, such as stainless steel. Coatings such asTeflon may be added to protect the materials in probe 11 from thechemicals used in semiconductor processing.

FIG. 2 depicts in a cross-sectional view the operation of the movableprobe 11 disposed over a portion of a semiconductor wafer 33. Thetransducer 13 is shown with the fluid flow indicated into thetransducer. The input port 19 receives the fluid and it is forciblyapplied through input port 19 to a central portion of the bottom opening23. The wafer surface closes the immersion hood formed by 17 and 15, andthe fluid and the particles picked up by the fluid circulate radiallyoutward from the central portion of the transducer. The fluid exits themovable megasonic probe 11 through the exhaust ports 21.

During processing, the transducer applies sonic energy which, as isknown, loosens particles from a film or surface on a semiconductorwafer. The wafer and wafer surface may be silicon or gallium arsenide,or an oxide or dielectric layer or passivation layer formed on thewafer, or a metal or conductor layer formed on the wafer. DIW may beapplied as a rinse or cleaner. Other fluids may be used including diluteammonia hydroxide hydrogen peroxide water mixture, or “dAPM”, sometimesknown as “SC1”. Solvents may be used, also gasses may be bubbled intosolution such as N2, NH3, H2, O3, and the like. Other chemicals such assurfactants may be added to the liquid to improve the cleaning process.

In alternative embodiments, the transducer 13 and immersion hood 15could be modified so that the liquid flow is reversed. In thisalternative embodiment, fluid is input into the outside ports 21 and theliquid flows radially inward to the central port 19 where it isexhausted. In either embodiment, the liquid is provided flowing acrossthe surface of the wafer 33 as the megasonic energy is applied, and theparticles loosened are immediately removed.

In operation, the transducer 13 applies sonic energy to loosen theparticles 36. As is known, ultrasonic energy could be used, which maylie in the frequency range from 1-20 Mhz, but in these exampleembodiments, megasonic energy, from 500-1000 kHz range, is used as ittends to be less damaging to delicate structures.

FIG. 3 depicts in a cross-sectional view a wafer cleaning station 51incorporating the embodiments. Movable probe 11 is placed on the surfaceof the wafer 33 and moves across the wafer surface. Transport mechanism12 provides the motion mechanically and may include speed control withinit to provide an adjustable scan speed. In the embodiment shown here asan illustrative and non-limiting example, the megasonic probe movesrectilinearly across the wafer; and the wafer support 35 rotates thewafer 33 about a central axis. The movable probe 11 may travel all theway across the wafer, or partially across the wafer, for example fromthe center of the wafer to and from the outside edge. Transportmechanism 12 may be an arm, beam or rail, and may move the movable probe11 by use of a stepper motor, rotors, worm gears, push rods, cables,hydraulics, spindles and the like. Only the bottom portion of movablemegasonic probe 11 contacts the wafer surface, and portions 17 at thebottom opening 23, as shown above. The wafer 33 may be supported at itsrim by supports 47 for example; slight vacuum, manual clamping pressureor electrostatic force might be used to secure the wafer 33 to support35.

In FIG. 3, for this non-limiting example embodiment, an optional waferbackside cleaning system is illustrated. Input port 43 receives fluidsfor cleaning the backside of the wafer 33. The liquids may be DIW ordAPM, for example. A chamber 45 is formed by the bottom surface of thewafer 33 and a portion of the support 35. The DIW circulates radiallyoutward from the center spindle 37 and exits the support 35 at outputports 39, as indicted by the arrows. In an alternative embodiment, theliquid flow could be reversed. Cleaning the backside in this fashion isconsidered a water dip or solvent dip, and improves overall particleremoval and wafer cleanliness; increasing performance of subsequentprocess steps. However, in alternative embodiments, wafer support 35 maybe provided without the backside cleaning portions.

In operation, the embodiments provide a movable probe that is veryadjustable in terms of scan speed and position. In an embodiment, thetransport mechanism may be arranged so that the movable probe may movein any x-y direction, or as shown in FIG. 3, the probe may move linearlyacross the wafer while the wafer rotates. The wafer rotation and probespeed are then adjusted together to form an adjustable scan speed. In analternative embodiment, contemplated herein and within the scope of theappended claims, the movable megasonic probe may be fixed to astationary position and the wafer support 35 can provide wafer movementin both rotation and linear directions. The relative scan speed of themovable megasonic probe across the surface of the wafer is what isimportant. It is not important how the motion is arranged but themovable probe 11 should be able to scan the entire wafer, and the scanspeed and position may be adjustable.

Different films that are to be cleaned on the surface of the wafer havedifferent characteristic hardness and durability. In operation, themovable probe 11 is adjusted to have different scan speeds depending onthe surface being cleaned and the liquids applied. For more durablesurfaces a more thorough cleaning may be used, while for more delicatestructures, care must be taken that the movable probe and the releasedparticles not cause damage. By adjusting the scan speed and times forthe cleaning, efficient particle removal for different materials iseasily accomplished using the embodiments.

The unique design of the movable probe of the embodiments also providesimmediate particle removal even as the particles are loosened by themegasonic energy in the fluid. FIG. 4 depicts the cleaning action thatoccurs during use of the embodiments. Arrows 55 indicate a “drag force”that is parallel to the surface of the substrate, which flows across thepattern 34 as the particles 36 are released by action of the megasonicenergy. The drag force is created by the design of megasonic probe 11,which has for example a radial outflow of the liquid from the center ofthe probe (not shown), flowing across the wafer surface and then beingremoved immediately away from the wafer. The drag force shown by arrows55 will move the particles 36 to the exhaust ports in the megasonicprobe and carry them directly away from the wafer, so that they will notre-deposit on the wafer.

FIG. 5 depicts a method embodiment in a flow diagram. In state 61, thewafer cleaning process begins by positioning the movable probe over aportion of the wafer surface. As described above the size of the movableprobe may vary but typically will cover a portion of the wafer surface.In state 63, megasonic energy is applied to the portion of the wafersurface beneath the megasonic probe, as is known, megasonic energy willloosen particles from the surface. In state 65, the cleaning liquid,which may be, without limitation, DIW, dAPM or SC1, solvents, gasbubbled into liquids, surfactants and the like, is applied to theportion of the wafer beneath the megasonic probe to remove particles andclean the surface. As described above, the liquid flows across thesurface and is removed through exhaust ports so that the particlesloosened by the megasonic energy are carried away. In state 67 themegasonic probe is moved in a scan pattern relative to the wafer so thatthe entire wafer surface may be cleaned. Note that the method flowdiagram in FIG. 5 presents an example order but these states areperformed more or less simultaneously or in any order, and are brokenout here only for sake of discussion and simplicity. The megasonic probesimultaneously applies liquid to the wafer surface, and appliesmegasonic energy to the surface; and moves across it at the same time,either by movement of the megasonic probe, or of the wafer, or both; sothat a relative scan speed is established between the wafer and themovable megasonic probe.

In an alternative method embodiment, the megasonic probe described abovemay be used to apply chemicals other than cleaning chemicals or rinsefluids. For example chemicals that are sometimes applied by sprayingcould be applied to the wafer surface using the movable probe of theembodiments as an immersion hood. A photoresist strip chemical is oneexample of such an application. Other chemicals may likewise be appliedusing the embodiments and these alternatives are contemplated as part ofthe embodiments and fall within the scope of the appended claims. Insuch an embodiment, the transducer may not be active, or may not bepresent if megasonic energy is not required.

In an embodiment, a method includes positioning a movable probe on awafer surface, the movable probe having an open bottom portion thatexposes a portion of the wafer surface; applying a liquid onto the wafersurface through a bottom portion of the movable probe; and moving themovable probe at a predetermined scan speed to traverse the wafersurface, applying the liquid to the wafer surface while moving over thewafer surface. In a further embodiment, a transducer is provided withinthe movable probe; and while moving the movable probe over the wafersurface, sonic energy is applied to the portion of the wafer surfacebeneath the bottom portion of the movable probe. In another embodiment,the movable probe has a central portion for applying the liquid to thewafer surface, the liquid flowing across the wafer surface, and theliquid being removed from the wafer surface continuously by exhaustports in the outer portion of the movable probe. In still anotherembodiment, applying the liquid further includes applying deionizedwater. In another method embodiment, applying the liquid furtherincludes applying one of deionized water, ammonia hydroxide-hydrogenperoxide, gas in solution, solvents and surfactants. In yet anotherembodiment, moving the movable probe further includes moving the movableprobe in a linear direction while the wafer is rotated about a centralaxis. In still another embodiment, moving the movable probe includesmoving the wafer in a linear direction while the wafer is rotated andthe movable probe remains stationary. In a further alternativeembodiment, moving the movable probe includes moving the movable probein at least two directions while the wafer remains stationary so as toscan the entire wafer. In still another alternate embodiment, the methodinclude supplying a liquid to a backside surface of the wafer oppositethe wafer surface, the liquid selected from deionized water, cleaners,solvents, gas in solution, and surfactants. In yet another embodiment,applying the sonic energy includes applying energy with a frequency ofbetween 500 and 1000 kHz. In a further embodiment, applying the sonicenergy includes applying energy greater than 500 kHz and less than 20Mhz.

In an embodiment, an apparatus includes a movable wafer probe, whichfurther includes a transducer disposed within a body forming animmersion hood, the body having sides surrounding the transducer andhaving an open bottom portion configured to be placed on a wafersurface; a liquid input port for receiving fluids to be applied to awafer surface at the open bottom portion; and liquid exhaust ports forremoving the liquid from the wafer surface through the open bottomportion. In a further embodiment, the transducer has a central openingthat forms a part of the liquid input port. In yet another embodiment,the transducer has an outside portion spaced from inner walls of thebody, the space between the outside portion of the transducer and theinner walls of the body forming the liquid exhaust ports. In yet anotherembodiment, the apparatus includes a transport mechanism for moving themovable megasonic probe. In still another embodiment, the transportmechanism moves the movable megasonic probe in a linear fashion. In analternative embodiment, the transport mechanism moves the movablemegasonic probe in at least two directions. In yet another embodiment,the transport mechanism provides an adjustable scan speed for moving themovable megasonic probe.

In still a further method embodiment, a method includes providing amovable probe, the movable probe having a megasonic transducer with acentral opening, a liquid input port coupled to the central opening, anopen bottom portion configured for applying liquid to a portion of awafer surface lying beneath the open bottom portion, liquid exhaustports configured for removing liquid from a portion of a wafer surface,the movable probe having a transport mechanism for moving the movableprobe across the wafer surface at a predetermined scan speed;positioning the movable probe on a wafer surface; applying a liquidreceived at the liquid input port of the movable probe onto a portion ofthe wafer surface lying beneath the open bottom portion, whilesimultaneously applying megasonic energy to the portion of the wafersurface. The method continues by removing the liquid from the portion ofthe wafer surface using the liquid exhaust ports of the movable probe;and moving the movable probe at a predetermined scan speed to traversethe wafer surface, applying the liquid and the megasonic energy to thewafer surface while moving over the wafer surface. During the methodparticles released by the megasonic energy applied to the wafer surfaceare carried away from the wafer surface by the liquid through theexhaust ports of the movable probe. In another method embodiment, theabove method also includes applying a liquid to a backside of the waferopposite the wafer surface.

The scope of the present application is not intended to be limited tothe particular illustrative embodiments of the structures, methods andsteps described in the specification. As one of ordinary skill in theart will readily appreciate from the disclosure of the presentinvention, processes, or steps, presently existing or later to bedeveloped, that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses or steps.

1. A method, comprising: positioning a movable probe on a wafer surface,the movable probe having an open bottom portion that exposes a portionof the wafer surface; applying a liquid onto the wafer surface throughthe open bottom portion of the movable probe; and moving the movableprobe at a predetermined scan speed to traverse the wafer surface,applying the liquid to the wafer surface while moving over the wafersurface.
 2. The method of claim 1, and further comprising: providing atransducer within the movable probe; and while moving the movable probeover the wafer surface, applying sonic energy to the portion of thewafer surface beneath the bottom portion of the movable probe.
 3. Themethod of claim 1, wherein the movable probe has a central portion forapplying the liquid to the wafer surface, the liquid flowing across thewafer surface, and the liquid being removed from the wafer surfacecontinuously by exhaust ports in the outer portion of the movable probe.4. The method of claim 1, wherein applying the liquid further comprisesapplying deionized water.
 5. The method of claim 1, wherein applying theliquid further comprises applying one selected from the group consistingessentially of deionized water, ammonia hydroxide-hydrogen peroxide, gasin solution, solvents and surfactants.
 6. The method of claim 1, whereinmoving the movable probe further comprises moving the movable probe in alinear direction while the wafer is rotated about a central axis.
 7. Themethod of claim 1, wherein moving the movable probe comprises moving thewafer in a linear direction while the wafer is rotated and the movableprobe remains stationary.
 8. The method of claim 1 wherein moving themovable probe comprises moving the movable probe in at least twodirections while the wafer remains stationary so as to scan the entirewafer surface.
 9. The method of claim 1 and further comprising: applyinga liquid to a backside surface of the wafer opposite the wafer surface,the liquid selected one from the group consisting essentially ofdeionized water, cleaners, solvents, gas in solution, and surfactants.10. The method of claim 2 wherein applying the sonic energy comprisesapplying energy with a frequency of between 500 and 1000 kHz.
 11. Themethod of claim 2 wherein applying the sonic energy comprises applyingenergy greater than 500 kHz and less than 20 Mhz.
 12. An apparatus,comprising: a movable wafer probe, comprising: a transducer disposedwithin a body forming an immersion hood, the body having sidessurrounding the transducer and having an open bottom portion configuredto be placed on a wafer surface; a liquid input port for receivingfluids to be applied to a wafer surface at the open bottom portion; andliquid exhaust ports for removing the liquid from the wafer surfacethrough the open bottom portion.
 13. The apparatus of claim 12, whereinthe transducer has a central opening that forms a part of the liquidinput port.
 14. The apparatus of claim 12, wherein the transducer has anoutside portion spaced from inner walls of the body, the space betweenthe outside portion of the transducer and the inner walls of the bodyforming the liquid exhaust ports.
 15. The apparatus of claim 12 andfurther comprising a transport mechanism for moving the movable waferprobe.
 16. The apparatus of claim 15 wherein the transport mechanismmoves the movable wafer probe in a linear fashion.
 17. The apparatus ofclaim 15 wherein the transport mechanism moves the movable wafer probein at least two directions.
 18. The apparatus of claim 15 wherein thetransport mechanism provides an adjustable scan speed for moving themovable wafer probe.
 19. A method, comprising: providing a movableprobe, the movable probe having a megasonic transducer with a centralopening, a liquid input port coupled to the central opening, an openbottom portion configured for applying liquid to a portion of a wafersurface lying beneath the open bottom portion, liquid exhaust portsconfigured for removing liquid from a portion of a wafer surface, themovable probe having a transport mechanism for moving the movable probeacross the wafer surface at a predetermined scan speed; positioning themovable probe on a wafer surface; applying a liquid received at theliquid input port of the movable probe onto a portion of the wafersurface lying beneath the open bottom portion, while simultaneouslyapplying megasonic energy to the portion of the wafer surface; removingthe liquid from the portion of the wafer surface using the liquidexhaust ports of the movable probe; and moving the movable probe at apredetermined scan speed to traverse the wafer surface, applying theliquid and the megasonic energy to the wafer surface while moving overthe wafer surface; wherein particles released by the megasonic energyapplied to the wafer surface are carried away from the wafer surface bythe liquid through the exhaust ports of the movable probe.
 20. Themethod of claim 19, and further comprising: applying a liquid to abackside of the wafer opposite the wafer surface.